(a) The following substances are placed in separate, identical long rods: dry wood, sea water, glass, and hydrogen gas at room temperature. Arrange them in increasing order of the speed with which a short sound pulse would travel through each rod.
(b) Give two qualitative reasons for the order you have written, making specific reference to the relative elasticity and density of the media.
(c) Even within the same substance—for example, two pieces of dry wood cut from different trees—the measured speed of sound may differ slightly. State and explain two possible factors that could cause such variations.